"Karaoke" systems with video disk reproduction are popular in recent years.
Such "karaoke" systems provide not only accompaniment of a requested music but also reproduce a video image matching o with the music. Some of these systems are provided with a video camera so that the video camera takes the picture of a singer and reproduces the picture on a TV screen.
By the way, when the video camera takes the picture of a singer (an object to be detected; hereinafter referred to simply as "object") who sings with "karaoke", the object may move frequently. In such a case, if the video camera is fixed, the object may step out of the imaging area of the camera, thereby not permitting accurate monitoring of the picture.
To overcome this shortcoming, a cameraman who operates the video camera must be involved. However, the "karaoke" systems are generally installed in restaurants, bars, or the like, and the cameraman following the object in the shop throughout the music bothers other guests, which is a large inconvenience.
To overcome such inconvenience, an imaging device for tracking an object (hereinafter referred to simply as "imaging device") such as shown in FIG. 1 has been proposed in, e.g., Japanese Patent Unexamined Publication No. 42169/1986.
As shown in FIG. 1, a video camera 2 is mounted on a stand 1 of the imaging device. A position detector 4 having an infrared light receiving lens 3 is mounted on the video camera 2.
On the other hand, an infrared light projecting unit 7 is provide on a shoulder 6 of an object 5.
The principle of detecting the position of the object 5 by the thus constructed imaging device is as shown in FIG. 2. That is, infrared light receiving units 7A to 7D are disposed so as to cross on a plane I. A plane II shows an area over in which the object 5 moves. When the level of the detected infrared light of, e.g., the infrared light receiving unit 7C or 7D is increased as the object 5 has moved, the movement of the object 5 is detected in an X-axis direction on the plane II. As a result, the stand 1 causes the video camera 2 to move in the X-axis direction, so that the object 5 is automatically tracked.
As a result of the construction, the automatic tracking of the object 5 contributes to dismissing the cameraman and dispenses with inconveniences of operating the video camera even in the case where a "karaoke" system is installed in a small space.
However, in the aforesaid conventional imaging device the optical axis L or R of the infrared light receiving unit 7D or 7C on the X axis in FIG. 2 is arranged so as to extend in parallel to each other as shown in, e.g., FIG. 3. This makes the areas A, B, C of the light receiving plane different as shown in FIG. 4, thereby causing errors in detecting the object 5, not allowing correct tracking of the object 5.
Further, with respect to the distance information of a background, an image to be obtained by a video camera is two-dimensional just like a photograph, while the actual background is three-dimensional.
Incidentally, a man collects distance information from subtle differences of two images visualized by two eyes. Similarly, in an artificial vision, three-dimensional information collected from two images obtained by two cameras is called "binocular stereoscopic vision". Having the problem of taking too much time in image processing such as obtaining points corresponding to the two images, there is no such artificial vision that has so far been put to practical use.
A technique that is often employed is to inject a slit light beam or spot light beam obliquely to a background or the like and obtain the information from horizontal deviations of optical points from the background or the like within the image. A device used for this is called a range finder.
However, in this technique, the distance information varies depending on the point onto which the slit light beam or spot light beam is injected, thereby causing conspicuous errors in distance detection. The tracking of a moving object is difficult, thus leading to errors in distance detection or the like.
Further, a light receiving device 100 such as shown in FIG. 5 has heretofore been used as an infrared light receiving device. The light receiving unit 100 consists of a light receiving element 101 and an antenna 102. The antenna 102 is of a type such that infrared light rays are reflected from the light receiving element that is disposed at the center to increase the light receiving level and thereby increase the sensitivity.
However, such antenna 102 does not provide a consistent directivity pattern, exhibiting such a variation as shown in FIG. 6. To utilize the directivity of the light receiving element in place of the antenna 102, the light receiving element must be modified.
As shown in FIG. 6, the light receiving level exhibits a large fluctuation, and its directivity is not consistent. If two such light receiving units are disposed so as to cause their light receiving areas to overlap one upon the other, it is difficult to identify the position of a light projecting unit.
Further, as shown in FIG. 7, if antennas 103, 104 are disposed adjacent to each other so that the light receiving planes of two of their light receiving units overlap one upon the other, a dead zone 105 occurs due to the thicknesses of the antennas 103, 104. Thus, when infrared light rays from a light projecting unit are injected to the dead zone, such zone cannot be identified.
If each of the antennas 103, 104 is made thinner, it is difficult to mount a light receiving element 106.